Immunoreactivities of gastrin (G-) cells. II. Non-specific binding of immunoglobulins to G-cells by ionic interactions.

Various gastro-entero-pancreatic (GEP) endocrine cells have been shown to contain concomitantly immunoreactivities against several peptide hormones. In the present study the "immunoreactivities" of gastrin (G-) cells of the rat stomach against 21 specific antisera and 10 control sera were investigated by means of the unlabelled antibody enzyme (PAP) technique using modifications of single steps in the immunocytochemical staining sequence. The results indicate that immunoglobulins can bind to gastrin cell granules obviously by non-specific ionic interactions. This non-specific binding of immunoglobulins occurs even in dilution ranges of the sera commonly used in immunohistochemical investigations of the GEP endocrine system. Since "adsorption controls" (preadsorption of the antisera with their respective antigens) will not discriminate between specific and non-specific binding of immunoglobulins to GEP endocrine cells additional specificity controls are necessary. In contrast to the immunostaining of various GEP endocrine cells by "established" antisera and of G-cells by gastrin antiserum immunoglobulins of sera from non-immunized animals as well as antibodies against corticotropin-lipotropin related peptides could be displaced from their binding sites in G-cells by alterations of the NaCl content of the buffers used as diluents or as rinsing solutions. To exclude immunostaining of GEP endocrine cells by nonspecific binding of immunoglobulins the following working procedures are recommended for immunocytochemical investigations of these cells: 1. Use of high titer antisera at low concentrations (diluted 1:1,500 or more). 2. Elevation of the salt (NaCl) content up to 0.5 M of the buffer used as diluent or as rinsing solution. 3. Adsorption controls will show reliable results only if point 1. and 2. have been taken into account.